Radio communication systems when designed for specific telecommunications markets, such as messaging and paging, are ordinarily designed to utilize simulcast techniques. Simulcast is a cost effective and fundamental feature required for the wide area delivery of today's messaging protocols to large service areas with thousands of roaming subscriber devices. It allows for the transmission of the protocols to reach into areas and buildings not easily accessible by other technologies, while providing additive signal levels in over-lapping service areas. A fundamental precept is that each transmitter in a region will send data with symbol transitions occurring very close to the same time mark as symbol transitions from adjacent transmitters. Precisely how close is dependent on constraints of the signaling stream utilized, distances between transmitters in the system, tolerable delay spread, error budgets, etc. For the transmitters to meet their portion of the allowable symbol transition tolerance, the time accuracy of the signal leaving the transmitting antenna must be controlled to within tens of microseconds or less.
Present radio communications systems often utilize Global Positioning System (GPS) receivers to provide both transmitter oscillator disciplining for transmitter stability and highly accurate simulcast synchronization for groups of overlapping transmitters. In addition to the use of GPS receivers for accurate timing, other highly accurate timing references have been used for similar purposes. These references include the use of T-Carrier span-line network clock references, Universal Time Coordinated (UTC) signals from High Frequency Single Side Band (HF-SSB) or Long Range Navigation (LORAN) receiver/synchronizers, or timing signals from a Cesium or Rubidium atomic clock reference. It should be noted that to ensure accurate synchronization among multiple over-lapping transmitters, the transmitters preferably use similar types of timing references. Since the above time references are expensive, it is desirable to minimize and/or replace them with less costly solutions.
Thus, what is needed is a method and apparatus for making relative timing adjustments for simulcast transmissions in a cost effective manner. The method and apparatus preferably should be transparent to system operation and equipment variances.